This invention relates to programmable logic devices (“PLDs”) such as those sometimes known as field programmable gate arrays (“FPGAs”). More particularly, the invention relates to input and/or output circuitry for differential signaling by such devices.
Differential signaling is increasingly of interest for use in interconnecting various devices in electronic systems. For example, such signaling may be used for high-speed serial communication between two or more integrated circuit devices on a printed circuit board.
It can happen in such uses of differential signaling that the polarities of the two differential input or output pins on one of the devices are reversed relative to what they are supposed to be. This can happen, for example, as a result of an error or misunderstanding in the design or fabrication of the device, or in the design or fabrication of the printed circuit board on which the devices are mounted. Even if there is no such error or misunderstanding, there can be situations in which it would be desirable to be able to reverse the polarity of a device's differential signaling input and/or output pins. For example, this could help to simplify the pattern of printed circuit board wiring traces connecting two or more devices on the printed circuit board.